1. Field of the Invention
The present invention relates to an AC/DC voltage converter, and more specifically, to an AC/DC voltage converter including a rectifier circuit connected to the inputs of a step-up converter circuit and a storage capacitor and a resistor connected to the outputs of the step-up converter circuit.
2. Description of the Related Art
In conventional voltage converters, a storage capacitor is connected directly to the outputs of a step-up converter circuit, while a resistor is either connected between one output of a rectifier circuit and one input of the step-up converter circuit or is connected to an input of the rectifier circuit.
The step-up converter circuit in such conventional voltage converters typically includes an inductor, an electronic switch and a diode or another switch. The switch in the step-up converter circuit permits actively influencing the time variation of the input current of the rectifier circuit. The rectifier circuit is preferably formed by a rectifier bridge. The pulse duty ratio of the switch is controlled such that the mean value of the input current of the rectifier circuit is proportional to the input voltage. This gives an essentially sinusoidal variation of the current. The resistor is necessary because the step-up converter circuit operates only when the output voltage at the storage capacitor is higher than the input voltage of the rectifier. Thus, the resistor limits the current during start-up, as the step-up converter can only work properly if the output voltage across the storage capacitor is larger than the input voltage to the rectifier. However, the input current flows through the resistor regardless of the position of the switch in the step-up converter. This leads to a correspondingly high power loss in the voltage converter.
FIG. 1 (PRIOR ART) shows a circuit arrangement for a conventional AC/DC voltage converter. The voltage converter includes a rectifier circuit 11, a resistor 5, a step-up converter circuit 12, and a storage capacitor 9. Rectifier circuit 11 includes two input terminals 13 and 14 and two output terminals 15 and 16. Step-up converter circuit 18 also includes two input terminals 17 and 18 and two output terminals 19 and 21. A.C. voltage source 20 is connected to the two input terminals 13 and 14 of rectifier circuit 11 and delivers an input voltage V.sub.i which produces an input current I.sub.i through rectifier circuit 11. Rectifier circuit 11 includes four diodes 1, 2, 3 and 4 disposed in a bridge circuit. Rectifier circuit 11 is connected to step-up converter circuit 12 through resistor 5. Output terminal 15 of rectifier circuit 11 is connected to an input of resistor 5, and an output of resistor 5 is connected to input terminal 17 of step-up converter circuit 12. Terminals 16 and 18 are directly connected to each other.
Step-up converter circuit 12 includes an inductor 6, a high-frequency switch 7, and a diode 8. Switch 7 connects inductor 6 with output terminal 16 of rectifier circuit 11. Diode 8 is connected to output terminal 19 of step-up converter circuit 12. The two output terminals 19 and 21 of step-up converter circuit 12 are connected to storage capacitor 9, across which an output voltage V.sub.o can be tapped, and which drives a load current I.sub.o to load 30. While switch 7 is closed, the current in inductor 6 increases, magnetic energy is stored in inductor 6, and diode 8 is off. If switch 7 is opened, the voltage across switch 7 increases until it surpasses the voltage across capacitor 9. Diode 8 starts to conduct the current stored in the inductor into storage capacitor 9. If the pulse duty-ratio of switch 7 is 0.5, i.e., the on-time and off-time of the switch are equal, then V.sub.o will equal 2V.sub.i. This conventional voltage converter, however, produces a relatively high power loss.